Photo-sensing device and manufacturing method thereof

ABSTRACT

A photo-sensing device includes a semiconductor substrate, a photosensitive device, a dielectric layer and a light pipe. The photosensitive device is in the semiconductor substrate. The dielectric layer is over the semiconductor substrate. The light pipe is over the photosensitive device and embedded in the dielectric layer. The light pipe includes a curved and convex light-incident surface.

BACKGROUND

Integrated circuits (ICs) with image sensors are used in a wide range ofmodern day electronic devices, such as, for example, cameras and cellphones. In recent years, complementary metal-oxide semiconductor (CMOS)image sensors have begun to see widespread use, largely replacingcharge-coupled device (CCD) image sensors. Compared to CCD sensors, aCMOS image sensor has many advantages such as low voltage operation, lowpower consumption, compatibility with logic circuitry, random access,and low cost. Some types of CMOS image sensors include front-sideilluminated (FSI) image sensors and back-side illuminated (BSI) imagesensors.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 to FIG. 8 are schematic cross-sectional views illustratingvarious stages in a manufacturing method of an image sensor according tosome embodiments of the present disclosure.

FIG. 9 to FIG. 14 are schematic cross-sectional views illustratingvarious stages in a manufacturing method of an image sensor according tosome embodiments of the present disclosure.

FIGS. 15A through 15D are enlarged views of the region R illustrated inFIG. 7 or FIG. 14 in accordance with various embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

FIG. 1 to FIG. 8 are schematic cross-sectional views illustratingvarious stages in a manufacturing method of an image sensor 10 accordingto some embodiments of the present disclosure. The image sensor 10 maybe, for example, a CMOS image sensor, and/or an integrated circuit (IC)die or chip.

Referring to FIG. 1, a semiconductor substrate 102 including a pluralityof active areas 104 is provided. Specifically, the semiconductorsubstrate 102 has a first surface 102 a and a second surface 102 bopposite to the first surface 102 a. A plurality of isolation structures106 are formed in the semiconductor substrate 102 and extend from thefirst surface 102 a of the semiconductor substrate 102 toward theinterior of the semiconductor substrate 102. In other words, theisolation structures 106 are formed to be embedded in the semiconductorsubstrate 102. In some embodiment, the isolation structures 106 may, forexample, be shallow trench isolation (STI) structures. The formationprocess of the isolation structures 106 may be attained by the followingsteps. First, a plurality of shallow trenches having a predetermineddepth are formed in the semiconductor substrate 102 by, for example,photolithograph/etching process or other suitable patterning processes.Then, a dielectric layer is deposited in the trenches. Subsequently, aportion of the dielectric layer is removed (e.g., polishing, etching, ora combination thereof) to form the isolation structures 106 (i.e. theSTI structures). In some alternative embodiments, the isolationstructures 106 may be deep trench isolation (DTI) structures, implantisolation structures, or other insulating structures to separate theactive areas 106.

In some embodiments, a material of the semiconductor substrate 102includes silicon, and a material of the isolation structures 106 (i.e.the STI structures) includes silicon oxide, silicon nitride, siliconoxynitride, other suitable materials, or a combination thereof. In somealternative embodiments, the semiconductor substrate 102 may be made ofsome other suitable elemental semiconductor, such as diamond orgermanium; a suitable compound semiconductor, such as gallium arsenide,silicon carbide, indium arsenide, or indium phosphide; or a suitablealloy semiconductor, such as silicon germanium carbide, gallium arsenicphosphide, or gallium indium phosphide.

As shown in FIG. 1, a plurality of photosensitive devices 108 are formedin the active areas 104. The photosensitive devices 108 are configuredto absorb radiation incident on the photosensitive devices 108 togenerate an electric signal. In some embodiments, the photosensitivedevices 108 are formed through ion implantation on the first surface 102a of the semiconductor substrate 102. For example, the photosensitivedevices 108 are photodiodes. Each of the photodiodes may include atleast one p-type doped region, at least one n-type doped region, and ap-n junction formed between the p-type doped region and the n-type dopedregion. In detail, when the semiconductor substrate 102 is a p-typesubstrate, n-type dopants (e.g., phosphorous or arsenic) may be dopedinto the active areas 104 of the semiconductor substrate 102 to formn-type wells, and the resulting p-n junctions in the active areas 104are able to perform the image sensing function. Similarly, when thesemiconductor substrate 102 is an n-type substrate, p-type dopants(e.g., boron or BF₂) may be doped into the active areas 104 of thesemiconductor substrate 102 to form p-type wells, and the resulting p-njunctions in the active areas 104 are able to perform the image sensingfunction. Detailed descriptions of ion implantation processes forforming n-type doped regions (wells) or p-type doped regions (wells) areomitted herein. When a reversed bias is applied to the p-n junctions ofthe photosensitive devices 108, the p-n junctions are sensitive to anincident light. The light received or detected by the photosensitivedevices 108 is converted into photo-current such that analog signalrepresenting intensity of the photo-current is generated. In somealternatively embodiments, the photosensitive devices 108 may be otherphotoelectric elements capable of performing image sensing function. Forexample, the photosensitive devices 108 may include a p-i-n junction,where an intrinsic semiconductor region may be arranged between andcontacting the n-type doped region and the p-type doped region.

In some embodiments, one or more transistors 109 may be formed on thefirst surface 102 a of the semiconductor substrate 102. The one or moretransistors 109 is designate for receiving signal originated from thephotosensitive devices 108. In some embodiments, the one or moretransistors 109, for example, may be transfer gate transistorsconfigured to selectively transfer charge accumulated in thephotosensitive devices 108 out of the photosensitive devices 108 forreadout. In some embodiments, other transistors (not shown) may also beformed on the first surface 102 a of the semiconductor substrate 102,such as source-follower transistors, row select transistors, resettransistors, or a combination thereof.

Referring to FIG. 2, an interconnection layer 200 is formed on the firstsurface 102 a of the semiconductor substrate 102. The interconnectionlayer 200 interconnects the transistors 109 (and/or other transistors)and other components (e.g., an analog-to-digital converter (ADC)) suchthat signal generated from the photosensitive devices 108 may betransmitted to other components for processing. In some embodiment, theinterconnection layer 200 includes a dielectric layer 210 and conductivewirings 220 in the dielectric layer 210. The dielectric layer 210 mayinclude an interlayer dielectric (ILD) layer 212 and a plurality ofinter-metal dielectric (IMD) layers 214, 216, 218 stacked over thesemiconductor substrate 102. The ILD layer 212 is formed on thesemiconductor substrate 102 to cover the photosensitive devices 108 andthe transistors 109. The IMD layers 214, 216, 218 are formed over theILD layer 212. In some embodiments, a material of the ILD layer 212 orthe IMD layers 214, 216, 218 may be, for example, silicon oxide, siliconnitride, silicon oxynitride, phosphosilicate glass (PSG),borophosphosilicate glass (BPSG), spin-on glass (SOG), fluorinatedsilica glass (FSG), carbon doped silicon oxide (e.g., SiCOH), polyimide,or a combination thereof. The conductive wirings 220 are electricallycoupled to devices (e.g., the transistors 109) on the first surface 102a of the semiconductor substrate 102. In some embodiments, a material ofthe conductive wirings 220 may be, for example, aluminum copper, copper,aluminum, some other conductive material, or a combination thereof. Itshould be noted that only one ILD layer and three IMD layers are shownherein. However, the disclosure is not limited thereto, and more ILDlayers or IMD layers may be provided.

As shown in FIG. 2, a topmost IMD layer (i.e., the IMD layer 218) amongthe plurality of IMD layers 214, 216, 218 has a thickness T1, and atleast one underlying IMD layer (i.e., the IMD layers 214 and/or 216)among the plurality of IMD layers 214, 216, 218 has a thickness T2.Since a subsequent process may reduce the thickness T1 of the topmostIMD layer (i.e., the IMD layer 218), in some embodiments, the thicknessT1 may be greater than the thickness T2 at this stage. The details willbe discussed later.

After forming the interconnection layer 200, a plurality of light pipes250 (shown in FIG. 6) configured to direct incident radiation towardsthe photosensitive devices 108 are then formed in the dielectric layer210. In some embodiments, the light pipes 250 are respectively disposedover the photosensitive devices 108. In some embodiments, the lightpipes 250 are arranged in an array. The fabrication of the light pipes250 is described in accompany with FIG. 3 through 6 in detail.

Referring to FIG. 3, trenches 230 are formed in the dielectric layer 210and over the photosensitive devices 108 by, for example,photolithograph/etching process or other suitable patterning processes.The trenches 230 extend from a top surface 210 a of the dielectric layer210 toward the interior of the dielectric layer 210. In someembodiments, bottom surfaces of the trenches 230 keep a distance d fromtop surfaces of the photosensitive devices 108 to prevent thephotosensitive devices 108 from damage causing by the formation processof the trenches 230 (e.g., etching process). In some embodiments, thedistance d between the bottom surfaces of the trenches 230 and the topsurfaces of the photosensitive devices 108 may range between about 40 nmand about 500 nm.

Referring to FIG. 4, a filling material 240 is formed on the dielectriclayer 210 to fill the trenches 230. In some embodiments, the fillingmaterial 240 is made of a high refractive index material. In someembodiments, a refractive index of the filling material 240 is higherthan a refractive index of the dielectric layer 210. In someembodiments, a material of the filling material 240 may be, for example,silicon nitride, tantalum oxide, or other suitable material. In someembodiments, the filling material 240 may entirely cover the top surface210 a of the dielectric layer 210 and entirely fill the trenches 230. Asillustrated in FIG. 4, the top surface of the filling material 240 ishigher than the top surface 210 a of the dielectric layer 210.Furthermore, the filling material 240 may have a substantially planartop surface. For instance, a distance between the top surface 210 a ofthe dielectric layer 210 and the top surface of the filling material 240is greater than about 0 micrometer and/or less than about 0.3micrometer. However, the disclosure is not limited thereto. In someembodiments, the distance between the top surface 210 a of thedielectric layer 210 and the top surface of the filling material 240 isgreater than about 0.3 micrometer. In one embodiment, the top surface210 a of the dielectric layer 210 and the top surface of the fillingmaterial 240 are substantially coplanar. In some other embodiments, thetop surface of the filling material 240 may not substantially planar,not shown.

Referring to FIG. 5 and FIG. 6, the filling material 240 is polished toform the light pipes 250 (shown in FIG. 6) in the trenches 230(illustrated in FIG. 3). Firstly, as shown in FIG. 5, the fillingmaterial 240 is polished until the top surface 210 a of the dielectriclayer 210 is revealed to form a polished filling material 242. In somealternative embodiments, the filling material 240 may be over-polishedslightly and the thickness of the dielectric layer 210 may be reducedslightly. In some embodiments, a portion of the filling material 240above the top surface 210 a of the dielectric layer 210 is removed so asto form the polished filling material 242 in the trenches 230(illustrated in FIG. 3), wherein a top surface 242 a of the polishedfilling material 242 is substantially at the same level with the topsurface 210 a of the dielectric layer 210. In some embodiments, thefilling material 240 is polished by a chemical mechanical polishing(CMP) process. Since the polished filling material 242 is formed by achemical mechanical polishing (CMP) process, the polished fillingmaterial 242 may include polishing marks distributed on the top surface242 a thereof.

Then, as shown in FIG. 5 and FIG. 6, the polished filling material 242and a portion of the dielectric layer 210 are further polished until thecurved and convex light-incident surfaces 250 a of the light pipes 250are formed. In some embodiments, the polished filling material 242(illustrated in FIG. 5) is polished with a first polishing rate, and theportion of the dielectric layer 210 is polished with a second polishingrate, wherein the second polishing rate is higher than the firstpolishing rate. In other words, at this stage, the polishing rate(removal rate) of the dielectric layer 210 is higher than the polishingrate (removal rate) of the polished filling material 242, so that thedielectric layer 210 is recessed more than the polished filling material242, and a periphery of the top surface 242 a of the polished fillingmaterial 242 may become rounded, thereby forming the curved and convexlight-incident surfaces 250 a of the light pipes 250. Since the lightpipes 250 is formed by a chemical mechanical polishing (CMP) process,the light pipes 250 may include polishing marks distributed on theconvex light-incident surfaces 250 a thereof.

In some embodiments, during the above-mentioned polishing process, aportion of the IMD layer 218 is removed, so that the thickness of theIMD layer 218 is reduced. In some embodiments, after polishing thepolished filling material 242 and the dielectric layer 210, thethickness T3 of the IMD layer 218 is substantially equal to thethickness T2 of at least one of the underlying IMD layers 214 and 216.Specifically, in order to make the thicknesses T3 of the IMD layer 218substantially the same as the thickness T2 of at least one of theunderlying IMD layers 214 and 216 after the polishing process, aninitial thickness (i.e., thickness T1) of the IMD layer 218 may begreater than an originally-designed thickness of an IMD layer before thepolishing process. Therefore, when the light pipes 250 are formed, thethickness T3 of the IMD layer 218 may be reduced to theoriginally-designed thickness (e.g., thickness T2) of an IMD layer.However, in some alternative embodiments, the thickness T3 of the IMDlayer 218 may be less than the thickness T2 of at least one of theunderlying IMD layers 214 and 216. In some alternative embodiments, thethickness T3 of the IMD layer 218 may be greater than the thickness T2of at least one of the underlying IMD layers 214 and 216.

As shown in FIG. 6, the light pipes 250 are formed over thephotosensitive devices 108 and embedded in the dielectric layer 210. Insome embodiments, the light pipes 250 extend into the dielectric layer210 of the interconnection layer 200, and the light pipes 250 and thephotosensitive device 108 are spaced apart by a portion of thedielectric layer 210. In some embodiments, the light pipes 250 arebetween adjacent conductive wirings 220 of the interconnection layer200. In some embodiments, each of the light pipes 250 includes alight-guiding portion 252 embedded in the dielectric layer 210 and alens portion 254 protruding upwardly from the light-guiding portion 252,the light-guiding portion 252 is between the lens portion 254 and thephotosensitive device 108, and the lens portion 254 includes the curvedand convex light-incident surface 250 a. In some embodiments, a height Hof the lens portion 254 may range between about 10 nm and about 500 nm.In some embodiments, the light-guiding portions 252 of light pipes 250may have tapered sidewalls 252 a, and the width of the light-guidingportions 252 is gradually decreased form a side close to the lensportions 254 to a side close to the photosensitive devices 108. However,in some alternative embodiments, the light-guiding portions 252 may havevertical sidewalls.

Since the light-guiding portion 252 and the lens portion 254 areintegrally formed and made of the same material, the lens portion 254 isseamlessly connected to the light-guiding portion 252. In other words,there is no interface between the light-guiding portion 252 and the lensportion 254. In some embodiments, an optical axis OA of the lens portion254 is substantially aligned with a center of the light-guiding portion252. That is to say, the lens portion 254 and the light-guiding portion252 share a same central axis CA. Therefore, a light collection may beimproved, so as to enhance the quantum efficiency. In addition, in someembodiments, the central axis CA of one light pipe 250 may besubstantially aligned with a center of one photosensitive device 108.

In some embodiments, the refractive index of the light pipe 250 ishigher than the refractive index of the dielectric layer 210, and theincident radiation may be totally internally reflected at the sidewalls252 a of the light-guiding portions 252, so as to guide incidentradiation to the photosensitive device 108. In some embodiments, therefractive index of the light pipe 250 may range between about 1.9 andabout 2.0. In some embodiments, the refractive index of the dielectriclayer 210 may be about 1.4. Besides, the lens portions 254 of the lightpipes 250 have the curved and convex light-incident surfaces 250 a toconverge the incident radiation. Therefore, the light pipe 250 havingthe light-guiding portion 252 and the lens portion 254 may enhance theradiation received by the photosensitive device 108.

Referring to FIG. 7, a planarization layer 262 is formed on thesemiconductor substrate 102 to cover the interconnection layer 200 andthe light pipes 250. In some embodiments, the planarization layer 262may be formed by depositing a dielectric material on the interconnectionlayer 200 and the light pipes 250 and then optionally planarizing thedielectric material. In some embodiments, the planarization layer 262may protect the lens portions 254 of the light pipes 250 and provide aplanar surface for the overlying layers.

FIGS. 15A through 15D are enlarged views of the region R illustrated inFIG. 7 in accordance with various embodiments of the present disclosure.In some embodiments, as shown in FIG. 15A to FIG. 15C, a maximum widthof the lens portion 254 may be substantially equal to that of thelight-guiding portion 252, and the lens portion 254 may entirely coverthe light-guiding portion 252. In FIG. 15A and FIG. 15B, the sidewall252 a of the light-guiding portion 252 may be in contact with thedielectric layer 210, and the curved and convex light-incident surfaces250 a may be in contact with and covered by the planarization layer 262.In FIG. 15A and FIG. 15C, the top surface 210 a of the dielectric layer210 is substantially planar. In FIG. 15B, a portion of the top surface210 a of the dielectric layer 210 in proximity to the light pipe 250 iscurved and concaved. In FIG. 15C, a sidewall 252 a of the light-guidingportion 252 may be in contact with the dielectric layer 210 and theplanarization layer 262, and the curved and convex light-incidentsurfaces 250 a may be in contact with the planarization layer 262. Inother words, after the light pipe 250 is formed, an upper portion of thelight-guiding portion 252 may protrude beyond the top surface 210 a ofthe dielectric layer 210 and in contact with the planarization layer262. Furthermore, an upper portion of the sidewalls 252 a of thelight-guiding portion 252 is covered by and in contact with theplanarization layer 262.

In some alternative embodiments, as shown in FIG. 15D, the lens portion254 may be wider than the light-guiding portion 252, and the lensportion 254 may not only entirely cover the light-guiding portion 252,but also cover a portion of the top surface 210 a of the dielectriclayer 210. In other words, the dielectric layer 210 is partially coveredby the lens portion 254. For example, the bottom dimension of the lensportion 254 may be wider than the top dimension of the light-guidingportion 252, and the lens portion 254 may entirely cover thelight-guiding portion 252 and partially cover a portion of the topsurface 210 a of the dielectric layer 210. In FIG. 15D, a sidewall 252 aof the light-guiding portion 252 may be in contact with the dielectriclayer 210, the curved and convex light-incident surfaces 250 a may be incontact with the planarization layer 262, and a bottom surface 254 a(e.g., a ring shaped bottom surface) of the lens portion 254 is incontact with a portion of the top surface 210 a of the dielectric layer210, wherein the bottom surface 254 a of the lens portion 254 isconnected between the curved and convex light-incident surfaces 250 a ofthe lens portion 254 and the sidewall 252 a of the light-guiding portion252.

Referring to FIG. 8, a passivation layer 264 and a plurality of colorfilters 266 (e.g., a red color filter, a blue color filter, a greencolor filter, etc.) may be formed on the planarization layer 262. Insome embodiments, the color filters 262 are respectively disposed overthe light pipes 250. In some embodiments, the color filters 266 arearranged in an array over the passivation layer 264. The color filters266 are respectively configured to transmit specific wavelengths ofincident radiation, while blocking other wavelengths of incidentradiation. For example, a color filter may be configured to pass redwavelengths of radiation, while blocking blue wavelengths of incidentradiation, whereas another color filter may be configured to pass bluewavelengths of radiation, while blocking red wavelengths of incidentradiation.

Further, a planarization layer 268 and a plurality of micro-lenses 270may be formed on the color filters 262. In some embodiments, themicro-lenses 270 are respectively disposed over the color filters 262.The micro-lenses 270 are configured to focus incident radiation (e.g.,photons) towards the light pipes 250. Each of the micro-lenses 270includes a convex shaped upper surface which facilitates the convergenceof the incident radiation. The micro-lenses 270 may be fabricated bymaterials such as silicon dioxide or a resin material on intermediatetransparent film. In some embodiments, the central axis CA of one lightpipe 250 may be substantially aligned with an optical axis of onemicro-lens 270.

In some embodiments, after the micro-lenses 270 are formed, thefabrication process of the image sensor 10 is completed. The imagesensor 10 may be, for example, front-side illuminated (FSI). In someembodiments, the image sensor 10 includes a plurality of photo-sensingdevices 100, and each of the photo-sensing devices 100 includes one ofthe photosensitive devices 108, one of the light pipes 250, one of thecolor filters 266 and one of the micro-lenses 270. In some embodiments,the photo-sensing devices 100 may be, for example, pixel sensors.

Since the light pipe 250 has the curved and convex light-incidentsurfaces 250 a to converge the incident radiation, there is no need tofurther form extra inner lenses between the light pipes 250 and themicro-lenses 270. Besides, another planarization layer formed on theextra inner lenses may be omitted. Accordingly, the image sensor 10including the light pipes 250 integrated with the lens portions 254 mayhave a simplified process, which facilitates to reduce cost and improveyield.

FIG. 9 to FIG. 14 are schematic cross-sectional views illustratingvarious stages in a manufacturing method of an image sensor according tosome embodiments of the present disclosure. Referring to FIG. 9, thedevice shown in FIG. 9 is similar to the device shown in FIG. 2. Thus,detailed descriptions thereof are omitted here. A differencetherebetween lies in that the thickness T1 of the IMD 218 issubstantially equal to the thickness T2 of the at least one of theunderlying IMD layers 214 and 216 since the light pipes 250 illustratedin the present embodiment is formed by a patterning process and a curingprocess instead of the polishing process. However, in some alternativeembodiments, the thickness T1 of the IMD layer 218 may be less than thethickness T2 of at least one of the underlying IMD layers 214 and 216.In some alternative embodiments, the thickness T1 of the IMD layer 218may be greater than the thickness T2 of at least one of the underlyingIMD layers 214 and 216.

Referring to FIG. 10, trenches 230 are formed in the dielectric layer210 and over the photosensitive devices 108 by, for example,photolithograph/etching process or other suitable patterning processes.The trenches 230 extend from a top surface 210 a of the dielectric layer210 toward the interior of the dielectric layer 210. In someembodiments, bottom surfaces of the trenches 230 keep a distance d fromtop surfaces of the photosensitive devices 108 to prevent thephotosensitive devices 108 from damage causing by the formation processof the trenches 230 (e.g., etching process). In some embodiments, thedistance d between the bottom surfaces of the trenches 230 and the topsurfaces of the photosensitive devices 108 may range between about 40 nmand about 500 nm.

Referring to FIG. 11, a filling material 240′ is formed on thedielectric layer 210 to fill the trenches 230. In some embodiments, thefilling material 240′ is made of a high refractive index material. Insome embodiments, a refractive index of the filling material 240′ ishigher than a refractive index of the dielectric layer 210. The fillingmaterial 240′ may include a photosensitive material, for example,polybenzoxazole (PBO), polyimide, benzocyclobutene (BCB) or the like,that may be patterned using a lithography mask. In some embodiments, thefilling material 240′ may entirely cover the top surface 210 a of thedielectric layer 210 and entirely fill the trenches 230. As illustratedin FIG. 11, the top surface of the filling material 240′ is higher thanthe top surface 210 a of the dielectric layer 210. Furthermore, thefilling material 240′ may have a substantially planar top surface. Forinstance, a distance between the top surface 210 a of the dielectriclayer 210 and the top surface of the filling material 240′ ranges fromabout 0.05 micrometer to about 1 micrometer. In some other embodiments,the top surface of the filling material 240′ may not substantiallyplanar, not shown.

Referring to FIG. 11 and FIG. 12, the filling material 240′ is patternedto form a patterned filling material 244. In some embodiments, thefilling material 240′ may be made of a photosensitive material, and thefilling material 240′ may be patterned by a photolithography process.The patterning process may be performed by exposing the filling material240′ to light and developing the filling material 240′ after theexposure. After the patterning process, spacing 246 is formed and thetop surface 210 a of the dielectric layer 210 is partially exposed.

Referring to FIG. 12 and FIG. 13, the patterned filling material 244 arethen reflowed and cured to form the light pipes 250. In someembodiments, a reflowing process is performed to re-shape the topprofile of the patterned filling material 244, and a curing process isthen performed to solidify the reflowed patterned filling material 244.After performing the above-mentioned reflowing and curing processes, aperiphery of a top surface 244 a of the patterned filling material 244may become rounded, thereby forming the curved and convex light-incidentsurfaces 250 a of the light pipes 250. In some embodiments, a topportion 244T of the patterned filling material 244 above the top surface210 a of the dielectric layer 210 may have a width W1 and a height H1,which may be specially designed to achieve specific curvature of thecurved and convex light-incident surfaces 250 a of the light pipes 250.In some embodiments, the width W1 of the top portion 244T of thepatterned filling material 244 may range between about 300 nm and about5000 nm. In some embodiments, the height H1 of the top portion 244T ofthe patterned filling material 244 may range between about 50 nm andabout 900 nm.

As shown in FIG. 13, the light pipes 250 are formed over thephotosensitive devices 108 and embedded in the dielectric layer 210. Insome embodiments, the light pipes 250 extend into the dielectric layer210 of the interconnection layer 200, and the light pipes 250 and thephotosensitive device 108 are spaced apart by a portion of thedielectric layer 210. In some embodiments, the light pipes 250 arebetween adjacent conductive wirings 220 of the interconnection layer200. In some embodiments, each of the light pipes 250 includes alight-guiding portion 252 embedded in the dielectric layer 210 and alens portion 254 protruding upwardly from the light-guiding portion 252,the light-guiding portion 252 is between the lens portion 254 and thephotosensitive device 108, and the lens portion 254 includes the curvedand convex light-incident surface 250 a. In some embodiments, a height Hof the lens portion 254 may range between about 50 nm and about 1000 nm.For example, the height H of the lens portion 254 is greater than theheight H1 of the top portion 244T of the patterned filling material 244(shown in FIG. 12). In some embodiments, the light-guiding portions 252of light pipes 250 may have tapered sidewalls 252 a, and the width ofthe light-guiding portions 252 is gradually decreased form a side closeto the lens portions 254 to a side close to the photosensitive devices108. However, in some alternative embodiments, the light-guidingportions 252 may have vertical sidewalls.

Since the light-guiding portion 252 and the lens portion 254 areintegrally formed and made of the same material, the lens portion 254 isseamlessly connected to the light-guiding portion 252. In other words,there is no interface between the light-guiding portion 252 and the lensportion 254. In some embodiments, an optical axis OA of the lens portion254 is substantially aligned with a center of the light-guiding portion252. That is to say, the lens portion 254 and the light-guiding portion252 share a same central axis CA. Therefore, a light collection may beimproved, so as to enhance the quantum efficiency. In addition, in someembodiments, the central axis CA of one light pipe 250 may besubstantially aligned with a center of one photosensitive device 108.

In some embodiments, the refractive index of the light pipe 250 ishigher than the refractive index of the dielectric layer 210, and theincident radiation may be totally internally reflected at the sidewalls252 a of the light-guiding portions 252, so as to guide incidentradiation to the photosensitive device 108. In some embodiments, therefractive index of the light pipe 250 may range between about 1.9 andabout 2.0. In some embodiments, the refractive index of the dielectriclayer 210 may be about 1.4. Besides, the lens portions 254 of the lightpipes 250 have the curved and convex light-incident surfaces 250 a toconverge the incident radiation. Therefore, the light pipe 250 havingthe light-guiding portion 252 and the lens portion 254 may enhance theradiation received by the photosensitive device 108.

Referring to FIG. 14, a planarization layer 262, a passivation layer264, a plurality of color filters 266, a planarization layer 268 and aplurality of micro-lenses 270 may be formed. The planarization layer262, the passivation layer 264, the plurality of color filters 266, theplanarization layer 268 and the plurality of micro-lenses 270 shown inFIG. 14 are similar to the planarization layer 262, the passivationlayer 264, the plurality of color filters 266, the planarization layer268 and the plurality of micro-lenses 270 shown in FIG. 8, and detaileddescriptions thereof are omitted here. Besides, enlarged views of theregion R in FIG. 14 is also shown in FIG. 15A to FIG. 15D, and detaileddescriptions thereof are not repeated herein.

Since the light pipe 250 has the curved and convex light-incidentsurfaces 250 a to converge the incident radiation, there is no need tofurther form extra inner lenses between the light pipes 250 and themicro-lenses 270. Besides, another planarization layer formed on theextra inner lenses may be omitted. Accordingly, the image sensor 10including the light pipes 250 integrated with the lens portions 254 mayhave a simplified process, which facilitates to reduce cost and improveyield.

In accordance with some embodiments of the disclosure, a photo-sensingdevice includes a semiconductor substrate, a photosensitive device, adielectric layer and a light pipe. The photosensitive device is in thesemiconductor substrate. The dielectric layer is over the semiconductorsubstrate. The light pipe is over the photosensitive device and embeddedin the dielectric layer. The light pipe includes a curved and convexlight-incident surface.

In accordance with some embodiments of the disclosure, a method ofmanufacturing a photo-sensing device includes at least the followingsteps. A semiconductor substrate including a photosensitive deviceformed therein is provided. A dielectric layer is formed over thesemiconductor substrate. A trench is formed in the dielectric layer. Afilling material is formed on the dielectric layer to fill the trench.The filling material and the dielectric layer are polished to form alight pipe in the trench, wherein the light pipe includes a curved andconvex light-incident surface.

In accordance with some alternative embodiments of the disclosure, amethod of manufacturing a photo-sensing device includes at least thefollowing steps. A semiconductor substrate is provided. A photosensitivedevice is formed in the semiconductor substrate. A dielectric layer isformed over the semiconductor substrate. A trench is formed in thedielectric layer. A filling material is formed on the dielectric layerto fill the trench. The filling material is patterned to form apatterned filling material. The patterned filling material is cured toform a light pipe in the trench, wherein the light pipe includes a lensportion having a curved and convex light-incident surface.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of fabricating a photo-sensing device,comprising: providing a semiconductor substrate comprising aphotosensitive device formed therein; forming a dielectric layer overthe semiconductor substrate; forming a trench in the dielectric layer;forming a filling material on the dielectric layer to fill the trench;and polishing the filling material and the dielectric layer to form alight pipe in the trench, wherein the light pipe comprises a curved andconvex light-incident surface, and polishing the filling material andthe dielectric layer comprises: polishing the filling material until thedielectric layer is revealed to form a polished filling material; andpolishing the polished filling material and a portion of the dielectriclayer until the curved and convex light-incident surface of the lightpipe is formed.
 2. The method according to claim 1, wherein the polishedfilling material is polished with a first polishing rate, the portion ofthe dielectric layer is polished with a second polishing rate, and thesecond polishing rate is higher than the first polishing rate.
 3. Themethod according to claim 1, wherein the dielectric layer comprises aplurality of inter-metal dielectric layers stacked over thesemiconductor substrate, a topmost inter-metal dielectric layer amongthe plurality of inter-metal dielectric layers has a first thickness, atleast one underlying inter-metal dielectric layer among the plurality ofinter-metal dielectric layers has a second thickness, and the firstthickness is greater than the second thickness before polishing thefilling material and the dielectric layer.
 4. The method according toclaim 3, wherein after polishing the filling material and the dielectriclayer, a portion of the topmost inter-metal dielectric layer is removed.5. The method according to claim 3, wherein after polishing the fillingmaterial and the dielectric layer, the thickness of the topmostinter-metal dielectric layer is substantially equal to that of the atleast one underlying inter-metal dielectric layer.
 6. A method offabricating a photo-sensing device, comprising: providing asemiconductor substrate comprising a photosensitive device; forming aninterconnect structure on the semiconductor substrate; forming a trenchin the interconnect structure; forming a filling material covering theinterconnect structure, wherein a refractive index of the fillingmaterial is higher than a refractive index of dielectric layers of theinterconnect structure; and partially removing the filling material andthe interconnect structure to form a light pipe in the trench through amulti-step polishing process, wherein the light pipe comprises a roundedlight-incident surface formed by chemical mechanical polishing.
 7. Themethod according to claim 6, wherein the filling material and theinterconnect structure are partially removed by a grinding process. 8.The method according to claim 6, wherein partially removing the fillingmaterial and the interconnect structure to form the light pipe in thetrench comprises: performing a first polishing process to remove a firstportion of the filling material until the dielectric layers of theinterconnect structure are revealed; and performing a second polishingprocess to remove a second portion of the filling material and a portionof the dielectric layers to form the light pipe having the roundedlight-incident surface.
 9. The method according to claim 8, wherein thesecond portion of the filling material is polished with a firstpolishing rate, the portion of the dielectric layers is polished with asecond polishing rate higher than the first polishing rate.
 10. Themethod according to claim 8, wherein a topmost dielectric layer amongthe dielectric layers has a first thickness before performing the secondpolishing process.
 11. The method according to claim 10, wherein atleast one underlying dielectric layer among the dielectric layers has asecond thickness, and the first thickness is greater than the secondthickness.
 12. The method according to claim 10, wherein the light pipeprotrudes from a top surface of the topmost dielectric layer among thedielectric layers after performing the second polishing process.
 13. Themethod according to claim 10, wherein the thickness of the topmostdielectric layer among the dielectric layers is substantially equal tothat of the at least one underlying dielectric layer among thedielectric layers after performing the second polishing process.
 14. Themethod according to claim 10, wherein the rounded light-incident surfacecomprises a curved and convex light-incident surface.
 15. The methodaccording to claim 10, wherein the light pipe comprises a light-guidingportion embedded in the dielectric layers and a lens portion over thelight-guiding portion.
 16. A method of fabricating a photo-sensingdevice, comprising: providing a semiconductor substrate comprising aphotosensitive device; forming a dielectric layer including a trenchover the semiconductor substrate; forming a filling material coveringthe dielectric layer and filling the trench; performing a firstpolishing process to remove a first portion of the filling materialuntil the dielectric layer is revealed; and performing a secondpolishing process to remove a second portion of the filling material anda portion of the dielectric layer to form a light pipe protruding fromthe dielectric layer, wherein the light pipe comprises a light-guidingportion embedded in the dielectric layer and a lens portion over thelight-guiding portion, and the lens portion comprises the roundedlight-incident surface formed by chemical mechanical polishing.
 17. Themethod according to claim 16, wherein the light pipe has a roundedlight-incident surface after performing the second polishing process.18. The method according to claim 16, wherein a refractive index of thefilling material is higher than a refractive index of dielectric layer.19. The method according to claim 16, wherein the second portion of thefilling material is polished with a first polishing rate, the portion ofthe dielectric layer is polished with a second polishing rate higherthan the first polishing rate.